1. Field of the Invention
The present invention relates to a reflecting sheet, and more particularly, to a reflecting sheet including a reinforcing layer of a backlight unit and a method of fabricating the reflecting sheet where a base sheet is divided into upper and lower division sheets and a reinforcing layer is formed on at least one of the upper and lower division sheets.
2. Discussion of the Related Art
As information age progresses, demand for display device displaying images has increased in various forms. Recently, various flat panel displays (FPDs) such as a liquid crystal display (LCD), a plasma display panel (PDP) and an organic light emitting diode (OLED) have been utilized. Among the various FPDs, a liquid crystal display (LCD) device has been widely used for a television or a monitor because of its advantages such as a small size, a light weight, a thin profile and a low power consumption. Since the LCD device is a non-emissive type display device, an additional light source is required. Accordingly, a backlight unit including a light source is disposed under the liquid crystal panel. The backlight unit may be classified into a direct type and an edge type according to a position of the light source.
In the direct type backlight unit, the light source is disposed under the liquid crystal panel and the light from the light source is directly supplied to the liquid crystal panel. In the edge type backlight unit, a light guide plate is disposed under the liquid crystal panel and the light source is disposed at a side of the light guide plate so that the light from the light source can be indirectly supplied to the liquid crystal panel using refraction and reflection in the light guide plate.
For the purpose of improving efficiency of light irradiated onto the liquid crystal panel, the edge type backlight unit includes a reflecting sheet that is disposed under the light guide plate to reflect the incident light from the light source.
FIG. 1 is an exploded perspective view showing a liquid crystal display device including an edge type backlight unit according to the related art. In FIG. 1, a liquid crystal display (LCD) device 10 includes a liquid crystal panel 40, a backlight unit 20, a main frame 70, a top frame 60 and a bottom frame 50.
The liquid crystal panel 40 and the backlight unit 20 are integrated by the main frame 70, the top frame 60 and the bottom frame 50. The main frame 70 surrounds an edge portion of the liquid crystal panel 40 and the backlight unit 20. In addition, the top frame 60 covers a front edge portion of the liquid crystal panel 40 and the bottom frame 50 covers a rear surface of the backlight unit 20.
First and second printed circuit boards (PCBs) 44 and 46 are connected to the liquid crystal panel 40 through a flexible circuit board (FPC) 42. The first and second PCBs 44 and 46 may be bent toward a side surface of the main frame 70 or a rear surface of the bottom frame 50 during the integration of the liquid crystal panel 40 and the backlight unit 20 by the main frame 70, the top frame 60 and the bottom frame 50.
The backlight unit 20 disposed under the liquid crystal panel 40 includes a fluorescent lamp 24, a lamp housing 30, reflecting sheet 22, a light guide plate 26 and a plurality of optical sheets 28. The fluorescent lamp 24 as a light source is disposed along at least one side of the main frame 70 to face a side surface of the light guide plate 26 and the lamp housing 30 wraps the fluorescent lamp 24. The reflecting sheet 22 disposed over the bottom frame 50 is integrated with the lamp housing 30 as one body. In addition, the plurality of optical sheets 28 are disposed over the light guide plate 26.
In the backlight unit 20, the light emitted from the fluorescent lamp 24 enters the side surface of the light guide plate 26 and is refracted toward the liquid crystal panel 40. The light passing through the light guide plate 26 is diffused or collimated in the plurality of optical sheets 28 so that the light having a uniform brightness can be supplied to the liquid crystal panel 40. A side of the main frame 70 corresponding to the fluorescent lamp 24 and the lamp housing 30 may be removed such that the main frame 70 has an open shape. In addition, the plurality of optical sheets 28 may include a prism sheet and a diffusing sheet.
FIG. 2 is a cross-sectional view showing a reflecting sheet for a backlight unit according to the related art. In FIG. 2, the reflecting sheet 22 includes a reflecting layer 22a, an upper surface layer 22b and a lower surface layer 22c. The reflecting layer 22a reflects light and includes a fine foam 80. The upper and lower surface layers 22b and 22c are disposed over and under the reflecting layer 22a, respectively, and protect the reflecting layer 22a. 
The light emitted from the fluorescent lamp 24 (of FIG. 1) is converted into a planar light by the light guide plate 26 (of FIG. 1) and the reflecting sheet 22 reflects the planar light toward the liquid crystal panel 40 using difference in refractive indices of the reflecting layer 22a and the air in the fine foam 80. The upper and lower surface layers 22b and 22c protecting the reflecting layer 22a do not include the fine foam 80.
FIG. 3 is a cross-sectional view showing a backlight unit according to the related art. In FIG. 3, the bottom frame 50 has a concave portion 50a and a flat portion 50b. The concave portion 50a may be formed in the bottom frame 50 to obtain a space for a wiring lines between the bottom frame 50 and the reflecting sheet 22 or a space for combining the bottom frame 50 and the main frame 70 (of FIG. 1). Since the concave portion 50a recedes from a flat portion 50b, a weight of the light guide plate 26 may be concentrated on a part of a boundary of the concave portion 50a when the light guide plate 26 is disposed over the bottom frame 50 with the reflecting sheet 22 interposed. For example, the weight of the light guide plate 26 may be concentrated on the part of the boundary of the concave portion 50a in a portion A. As a result, the boundary of the concave portion 50a of the reflecting sheet 22 may contact the light guide plate 26 and be pressed by the light guide plate 26 in the portion A, while the boundary of the concave portion 50a of the reflecting sheet 22 may be separated from the light guide plate 26 and not be pressed by the light guide plate 26 in a portion B.
FIGS. 4A and 4B are plan views showing a light guide plate in portions A and B, respectively, of FIG. 3. FIGS. 4A and 4B show a surface of the light guide plate 26 (of FIG. 3) when the fluorescent lamp 24 (of FIG. 1) is turned on. In FIG. 4A, the weight of the light guide plate 26 is concentrated on the boundary of the concave portion 50a (of FIG. 3) of the reflecting sheet 22 and the reflecting sheet 26 is pressed by the light guide plate 26 in the portion A. In FIG. 4B, the reflecting sheet 26 is not pressed by the light guide plate 26.
The light guide plate 26 includes a plurality of uniformity patterns 26a on a rear surface thereof to improve uniformity of the planar light. When the reflecting sheet 26 is not pressed by the light guide plate 26 as in FIG. 4B, the plurality of uniformity patterns 26a may contact the reflecting sheet 22 and the light guide plate 26 between adjacent uniformity patterns 26a may not contact the reflecting sheet 22. As a result, the light from the reflecting sheet 22 is scattered at the plurality of uniformity patterns 26a toward a space between the adjacent uniformity patterns 26a so that the brightness uniformity of the light having passed through the light guide plate 26 can be improved. Accordingly, the brightness of the plurality of uniformity patterns 26a increases and the brightness between the adjacent uniformity patterns 26a decreases so that the difference in brightness can be reduced.
When the reflecting sheet 22 is pressed by the light guide plate 26 as in FIG. 4A, the reflecting sheet 22 may contact the light guide plate 26 between adjacent uniformity patterns 26a as well as the plurality of uniformity patterns 26a. As a result, the light reflected by the reflecting sheet 22 may not be scattered to the space between the adjacent uniformity patterns 26a and may be focused on the plurality of uniformity patterns 26a. Accordingly, the brightness of the plurality of uniformity patterns 26a increases and the brightness between the adjacent uniformity patterns 26a decreases. The difference in brightness of the light guide plate 26 causes deterioration of the LCD device such as an image stain.
In the LCD device according to the related art, since the weight of the light guide plate is concentrated on the boundary of the concave portion of the bottom frame, the reflecting sheet is partially adsorbed onto the light guide plate and deterioration such as an image stain is caused by the partially pressed contact.
Further, the reflecting sheet has been required to various fields such as an LCD device, a solar cell and a lighting device. However, since production yield by the method of fabricating the reflecting sheet according to the related art has a limit, an additional investment in equipment is required for increase of production.